Precision engineering from Berg Propulsion has resulted in a substantial reduction in fuel consumption for a long-serving Baltic ropax.
This involved a propeller blade replacement, which Berg claimed can fit on any hub and also met the requirement to cut machinery vibrations.
’Stena Danica’ entered service in 1983 but, having been fully refurbished in 2005, remains operating on the shortsea link between Gothenburg (Sweden) and Frederikshavn (Denmark) making the crossing in three hours and 30 minutes.
Last year, Stena Line asked Berg Propulsion to revise the 154.9 m long ship’s twin propeller blades, with the aim of eliminating a persistent cavitation issue and enhancing fuel efficiency in a single project.
An additional technical challenge was that Berg’s solution needed to be reverse engineered to fit with the existing propeller hub originally manufactured by another industry player.
“Stena continuously reviews the performance of its ships to evaluate whether machinery and systems on board are optimal for their actual operations,” said Per Wimby, Senior Naval Architect, Stena Teknik.
“This is actually the third propeller blade replacement undertaken on ’Stena Danica’ over the years but this one is especially timely, given that it anticipates new regulatory requirements for all ships to demonstrate their energy efficiency.”
The ropax twin control pitch propellers are driven by two Sulzer 12ZV40 medium speed engines per shaft. After several months of commercial operations in multiple sea states, Wimby confirmed that by using the new propeller blades, average fuel consumption had been reduced, while neutralising a long standing issue with vibration. ”It is a balance between efficiency and comfort on board,” he explained.
Victor Abrahamsson, Berg Propulsion’s After Market Business Development, said that the blade design had been optimised to reflect a planned reduction in operating speeds, in a compromise between one engine per shaft line running at full power or two engines running per shaft, without ‘overpitching’.
“Blade geometry has moved on quickly in recent years, based on more accurate calculations, 3D scanning and better modelling tools. Today, we make better use of materials so that the same or enhanced efficiencies are achieved using slimmer profiles and blades which cover less area. It’s also much easier to evaluate and predict the relative performance of different blade types,” he said.
“With fuel consumption so high on the agenda, we are putting all available tools at the disposal of our owner clients to secure the efficiencies they need,” added Magnus Thorén, Energy & Efficiency Account Manager, Berg Propulsion.
“That means delivering tailor-made solutions for specific ship operating profiles, but this project also demonstrates what’s possible using the existing propeller hub: our designers and shipyard project teams could do this for any hub.”
“We would like to thank the whole Stena team for the very good co-operation to achieve the successful results for this project, as per our joint efforts,” commented Mattias Hansson, Berg’s Global Account Manager.